StackOverflow, bad enum value, self referencing properties. All great possible triggers for this error but how to find WHERE!
First of all forget IISExpress - that's just the 'messenger'.
I disabled IISExpress and ran my code in the console. Fortunately this gave me the extra message that wasn't appearing in Visual Studio when using iisexpress.
And for me it was a clumsy Stackoverflow (I added an overload recently but it called itself instead of the other method).
